1. Field of the Invention
The present invention pertains to a tool for testing chip-shaped electronic parts that do not have terminal lead wires, such as SMT devices, etc., and particularly to a platform for testing electronic parts that is appropriate for testing 3-terminal devices using high-frequency test signals. The present invention further pertains to an electrode structure for improving test stability.
2. Description of the Related Art
As is shown in FIG. 1, a conventional platform for testing 3-terminal SMT devices has clip means 12 that support the device under test (referred to below as the DUT) by sandwiching each terminal part of the device. Consequently, clip means 12 function as test electrodes and the test circuit shown in FIG. 2(a) is formed by connecting platform body 13 to a testing device (not shown) via testing device connector 14. However, by means of this structure, inductance L is produced by the length of the clip, as shown in the figure, and when this is combined with load capacities C""s of the DUT and resistance R of the clip, the combination forms impedance Z1, which is connected parallel to the resonator, i.e. the DUT, as shown in FIG. 2(b). This inductance L cannot be neglected when measuring impedance with high-frequency signals and therefore, creates errors in the measurement results of the DUT.
On the other hand, methods have also been adopted that alleviate the need of such error correction by testing a DUT directly soldered to a DUT board so that the test conditions will be the same as the conditions under which the DUT is used. In this case, the errors in the test data that are obtained are minimal. However, the form of connection to the testing device, which varies in accordance with the test parameters, varies with the type of DUT An example of a device that requires multiple forms of connection to a testing device is a ceramic resonator that is used for clock generation in various microcomputers. However, there are a total of three elements, two load capacities and 1 resonator, that are to be measured of subjects of this device, as shown in FIG. 2(a). In such a case, three forms of connections are necessary when these tests are performed, as shown in FIG. 3 (a DUT testing method by these 3 forms of connections is described in detail in Japanese Kokai Patent No. Hei 8(1996)-292,219). Consequently, in order to test each of the three elements, each of the these tests must require a specific DUT board with a different wiring from ones for the others.
Furthermore, using a switch box to switch the test path during testing, as disclosed in the previously filed Japanese Kokai Patent No. Hei 8(1996)-292,219, is well-known as a means for changing the form of connection of the DUT to the testing device. However, there are still the above-mentioned problems of inductance and anchoring the DUT to the electrodes when the DUT terminals are connected to the platform of the switch box.
Furthermore, test platforms for the above-mentioned soldering method not only have detrimental results in that the test procedure is complicated and costly, but also have the problem of being impossible to use the DUT as a final product if it is soldered to the test platform, such as a DUT board. Thus, they have the disadvantage of not being suitable for testing in mass-production lines.
Test platforms in which a DUT is mounted on an electrode group that has been set up on a test platform and a member that presses on the surface of the DUT opposite the surface that has made contact with the electrode group are generally known and are referred to herein as a conventional test platform with which DUTs can be interchangeably tested. Contact resistance between the DUT terminal and the electrodes on the test platform is often a problem related to the conventional test platform. This contact resistance has the tendency of not changing any lower after the surface pressure at this same contact surface exceeds a certain threshold value. Consequently, the method whereby a load applied to the DUT is increased so that the surface pressure reaches the threshold value in order to obtain the desired surface pressure is considered method of obtaining stable contact resistance. However, the electrode of SMT-type devices has a flat surface and it is difficult to obtain sufficient surface pressure with flat-surface electrodes on a conventional test platform. This surface pressure is generally found by dividing the load M pressing from DUT top surface by the surface area S of contact between DUT electrode and test platform electrode wherein the load M is limited to the allowable load to the DUT. On the other hand, it would appear that surface pressure would increase with a reduction in surface area S, but in the case of electrodes with a flat surface, the surface pressure when the terminal surface of the DUT contacts the flat surface of the electrode and the surface pressure when it touches the corner of the end of the electrode are generally very different and consequently contact resistance varies markedly with how the DUT is set up. If surface area S of this flat-surface electrode is too small, the DUT will disconnect from the electrode. Consequently, the minimum necessary surface area must be maintained for stable connection of the DUT to the platform and there is a limit to the allowable reduction of the surface area of a flat-surface electrode. Moreover, simply increasing the load, even if it is within the range of the allowable load to the DUT, will also lead to changes in measured values, and the pressing structure itself of the test platform will also be complex and large. Consequently, the necessary and sufficient contact surface pressure is not obtained, and it is difficult to retain reproducibility in test with the conventional structure under conditions where high-frequency microcurrent serves as the measurement signals.
Thus, in accordance with the prior art testing platform devices, there is a contradictory relationship between the exchangeability of DUTs and the improvement of accuracy and reproducibility of the test, and therefore, optimal means for solving the two issues simultaneously could not obtained.
Consequently, one object of the present invention is to provide a test platform in which inductance due to the length of the test electrode, which was a problem in the past, can be greatly reduced while being able to anchor DUTs interchangeably. Another object of the present invention is to easily provide multiple forms of connection of a DUT to a test device.
Yet another object of the present invention is to provide a test platform for testing electronic parts having a wide range of applications in which there are provided stable contact with various sizes and shapes of SMT devices.
Still another object of the present invention is to improve the structure of the electrodes, which are the electrical contact points of a DUT terminal, and thereby make simple and stable anchoring of the DUT to the test platform possible, and improve test reproducibility by stabilizing contact resistance.
The platform for testing electronic parts of the present invention has the following structure in order to achieve the above-mentioned objects: it has an electrode board, which has a plurality of electrode groups, each in an arrangement that corresponds to terminals of the device under test (DUT). The electrode groups are connected to the corresponding test circuit so that each terminal of the DUT is connected to the corresponding test circuit when the DUT is placed at each of multiple specific positions on the electrode board. A DUT guide means is provided, which holds the DUT and operates so that it changes the relative position of the DUT to the electrode board to travel the multiple specific positions. And a pressing means is provided, which presses the DUT to the electrode board and maintains electrical and mechanical contact between the terminals of the DUT and the electrode groups.
Moreover, by means of the platform for testing electronic parts of the present invention, the electrode board is anchored to the body of the platform for testing electronic parts, the DUT guide means has a sliding connection means that connects the DUT guide means to the body so that it can slide back and forth and has a DUT guide plate, in which an opening that matches the shape of the DUT is formed and with which the DUT is held inside the opening to demarcate the position of the DUT on the plane of movement, and the pressing means is connected to the DUT guide means and presses the top surface of the DUT toward the electrode board through the opening in the DUT guide plate.
Moreover, by means of the present invention, the pressing means has a load adjustment means for adjusting the load applied to the top surface of the DUT.
In addition, the platform for testing electronic parts of the present invention further has a means for retaining a desired relative position between the DUT guide means and the electrode board so that the DUT is placed at each of the multiple specific positions on the electrode board.
The platform for testing electronic parts of the present invention can further have three-dimensional shapes of electrodes (i.e., no-planar or -flat surfaces) forming the electrode groups of the same electrode board. For instance, at least one of the electrodes forming the electrode group can be provided with a spherical surface. The surface can also be shaped as a cylindrical shape.
In further detail, the electrode of the present invention can have the following structure: the electrode of the present invention is characterized in that it is anchored to a platform for testing electronic parts so that it projects from the top of the surface where a device under test (DUT) is set up, and in that the region that contacts a DUT is subject to elastic deformation when a load is applied under conditions such that the surface region capable of contacting the DUT forms a curved surface and the DUT is set up in the above-mentioned surface region. Moreover, in accordance with the present invention, the above-mentioned surface region of the electrode can be cylindrical in shape. The above-mentioned surface region can also be a spherical surface. Furthermore, one embodiment of the cylindrical electrode of the present invention is a cylindrical wire folded into an U-shaped form where the region of contact with the DUT is in the center block of the folded wire. Moreover, in an embodiment of the present invention having a spherical-surface electrode, the electrode is a pin-shaped member, the tip of which has a spherical surface, and the region of contact with the DUT is at the tip. Furthermore, by setting up a pressing mechanism for pressing the DUT to these electrodes using these electrode structures, it is possible to realize a platform for testing electronic parts with improved test stability. For example, by lining up two of the above-mentioned cylindrical electrodes in a row and placing one of the above-mentioned spherical electrodes at an equal distance from the ends of these electrodes that face one another, it is possible to stabilize a three-terminal device, and a platform for testing electronic parts that can cover devices of various sizes within a specific range can be realized.